Acetabular component migration in total HIP arthroplasty using CT and a semiautomated program for volume merging

Purpose: To develop a non-invasive method for detection of acetabular cup migration after total hip arthroplasty (THA) with a higher degree of accuracy than routine plain radiography.

Material and Methods: Two CT examinations, 10 min apart, were obtained from each of 10 patients that had undergone THA. Using an in-house developed semiautomated program for volume merging, the pelves in the two examinations were fused and the acetabular cup was visually and numerically evaluated to test the method's accuracy in detecting migration.

Results: In the visual evaluation of the best match a 1-mm translation of the cup was detectable. The numerical evaluation, comparing landmarks placed in the images of the acetabular cup and the head of the femur component in the two examinations, showed the mean difference in orientation of acetabular axes to be 2.5°, the mean distance between centre of cup face to be 2.5 mm and the mean distance between centre of the head of the prosthetic femoral component to be 1 mm.

Conclusion: This method has a significantly higher accuracy than routine plain radiography in detecting acetabular cup migration and could be used in clinical practice. It gives both a visual and a numerical correlate to migration.

Assessment of wear and periacetabular osteolysis using dual energy computed tomography on a pig cadaver to identify the lowest acceptable radiation dose

Objectives

Computed tomography (CT) plays an important role in evaluating wear and periacetabular osteolysis (PAO) in total hip replacements. One concern with CT is the high radiation exposure since standard pelvic CT provides approximately 3.5 millisieverts (mSv) of radiation exposure, whereas a planar radiographic examination with three projections totals approximately 0.5 mSv. The objective of this study was to evaluate the lowest acceptable radiation dose for dual-energy CT (DECT) images when measuring wear and periacetabular osteolysis in uncemented metal components.

Materials and Methods

A porcine pelvis with bilateral uncemented hip prostheses and with known linear wear and acetabular bone defects was examined in a third-generation multidetector DECT scanner. The examinations were performed with four different radiation levels both with and without iterative reconstruction techniques. From the high and low peak kilo voltage acquisitions, polychrmoatic images were created together with virtual monochromatic images of energies 100 kiloelectron volts (keV) and 150 keV.

Results

We could assess wear and PAO while substantially lowering the effective radiation dose to 0.7 mSv for a total pelvic view with an accuracy of around 0.5 mm for linear wear and 2 mm to 3 mm for PAO.

Conclusion

CT for detection of prosthetic wear and PAO could be used with clinically acceptable accuracy at a radiation exposure level equal to plain radiographic exposures.

Cite this article: B. Sandgren, M. Skorpil, P. Nowik, H. Olivecrona, J. Crafoord, L. Weidenhielm, A. Persson. Assessment of wear and periacetabular osteolysis using dual energy computed tomography on a pig cadaver to identify the lowest acceptable radiation dose. Bone Joint Res 2016;5:307–313. DOI: 10.1302/2046-3758.57.2000566.

Acetabular component migration in total hip arthroplasty using CT and a semiautomated program for volume merging

PURPOSE

To develop a non-invasive method for detection of acetabular cup migration after total hip arthroplasty (THA) with a higher degree of accuracy than routine plain radiography.

MATERIAL AND METHODS

Two CT examinations, 10 min apart, were obtained from each of 10 patients that had undergone THA. Using an in-house developed semiautomated program for volume merging, the pelves in the two examinations were fused and the acetabular cup was visually and numerically evaluated to test the method's accuracy in detecting migration.

RESULTS

In the visual evaluation of the best match a 1-mm translation of the cup was detectable. The numerical evaluation, comparing landmarks placed in the images of the acetabular cup and the head of the femur component in the two examinations, showed the mean difference in orientation of acetabular axes to be 2.5 degrees, the mean distance between centre of cup face to be 2.5 mm and the mean distance between centre of the head of the prosthetic femoral component to be 1 mm.

CONCLUSION

This method has a significantly higher accuracy than routine plain radiography in detecting acetabular cup migration and could be used in clinical practice. It gives both a visual and a numerical correlate to migration.

A versatile functional-anatomic image fusion method for volume data sets

We describe and validate a volumetric three-dimensional registration method, and compare it to our previously validated two-dimensional/three-dimensional method. CT/MRI and SPECT data from 14 patients were interactively fused using a polynomial warping technique. Registration accuracy was confirmed visually and by a nonsignificant F value from multivariate analysis of the transformed landmarks, a significant difference of the squared sum of intensity differences between the transformed/untransformed and the reference volume both at the 0.05 (p > 0.05) confidence level and an average 31% improvement of the correlation coefficient and cross correlation. For the two-dimensional/three-dimensional method, ROI center-to-center distance ranged from 1.42 to 11.32 mm (for liver) with an average of 6.13 mm +/- 3.09 mm. The average ROI overlap was 92.51% with a 95% confidence interval of 90.20-96.88%. The new method is superior because it operates on the true three-dimensional volume. Both methods give good registration results, take 10 to 30 min, and require anatomic knowledge.

The sociomoral reflection measure: applicability to Swedish children and adolescents

The Sociomoral Reflection Measure (SRM; Gibbs & Widaman, 1982) was developed as a group administerable instrument for measuring developmental stages of moral reasoning. The aim of this study was to examine its reliability and construct validity, employing a sample of 542 Swedish elementary and high school students (aged 8-17), from schools within metropolitan Stockholm. Interrater reliability varied between 0.83 and 0.92, and the internal consistency coefficient was 0.76. Factor analyses of the norms (on which the overall score is based) revealed one factor for the oldest age group (16-17 years), but two factors among the younger subjects (8-15 years), clearly separating the norms related to each of the two moral dilemmas. The Sociomoral Reflection Maturity Score was moderately, but significantly, related to both age and grade. The results suggests that, although used in a non-American context and with self-trained raters, the SRM seems highly applicable in Sweden, at least for research purposes.

An unusual complication following the removal of a neuroblastoma

A 17-month-old girl had a neuroblastoma with high preoperative urinary excretion of norepinephrine and a manifest hypertension. She developed during and after surgery circulatory complications similar to those seen when a pheochromocytoma is removed without prior sympathetic blockade. This complication in connection with a neuroblastoma has not been described previously. This case points to the necessity of careful preoperative evaluation of the circulatory function in cases of neuroblastomas in children. The paediatric surgeon and the anaesthetist should take a preoperative sympathetic blockade into consideration.